The present invention relates to an automatic lead feeding apparatus used in an automatic drafting machine, in which lead feeding apparatus pencil holders can be automatically exchanged mutually between a line drawing head and a writing instrument stocker provided at a side of a machine frame of the drafting machine.
According to an automatic lead feeding device described in Japan Patent Laid-open No. 1-78899, the device has a writing instrument stocker provided with a lead reservoir integrally installed with the stocker, and leads in the lead reservoir drop one by one by opening and closing a shutter mechanism in order to feed or supply the lead to a pencil holder held by the writing instrument stocker.
In addition, another similar device described in Japan Patent Laid-open 2-29399 has a pencil holder containing a plurality of writing leads. The pencil holder held by a writing instrument stocker is taken out by a sliding member and moved to another position. At the position, knocks are applied to the pencil holder by means of a knocking device.
The conventional automatic lead feeding mechanism having a pencil holder containing a plurality of writing leads has the drawback that the pencil holder must be large and heavy. Consequently, it is not suitable for high speed drawing or for precise control.
Another mechanism in which the writing instrument stocker and the lead reservoir are integrally assembled has another drawback in that it is impossible to feed leads or change pencil holders of the stocker during a drawing operation of the automatic drafting machine.
It is the purpose of the present invention to provide an automatic lead feeding apparatus without the drawbacks mentioned above concerning the prior art.
It is another purpose of the present invention to provide an automatic lead feeding apparatus able to freely combine various kinds of leads.